Two gene families essential for early eye development in different systematic groups are being studied. Homologs of the Drosophila eyes absent gene were identified in vertebrates (human, mouse, and chicken) as well as in molluscs (squid) and nematodes (C. elegans) phyla. One of the two identified mouse genes, Eab1, shows a specific, dynamic expression pattern during development. It is highly expressed in primary lens fibers and in the elongating secondary fibers and present, to a lesser extent, in retina and cornea. The Eab1 gene was mapped to mouse chromosome 2 near the cataract mutation Lop4 and to human chromosome 20q13. The homeobox-containing gene, Prox-1, is being studied in vertebrates. By in situ hybridization and immunohistochemistry, Prox-1 mRNA and its corresponding protein were detected mainly in the fiber cells of the developing lens and in the horizontal cells of the retina. Evidence was obtained that Prox-1 is a DNA-binding protein that may be involved in the regulation of some crystallin genes. The Prox-1 gene was mapped to human chromosome 1q32.2-q32.3 and to mouse chromosome 1, near retina degeneration mutation rd3. A second human gene, Prox-2, was identified and mapped to chromosome 14q24.3.